Connection-oriented data networks transmit data from point to point within the network along connections. These connections may be established along fixed paths or routes from a source node to a destination node within the network. The connections may be set up physically, for example in optically routed networks, or virtually, for example in Asynchronous Transfer Mode (ATM) networks or Multi Protocol Label Switching (MPLS) networks. Virtual connection-oriented networks are also termed permanent virtual circuit (PVC) networks.
Besides a routing that is specified for each connection, a connection might be controlled by a specified bandwidth admission level. If an admission level is set for a connection, then the source node of the connection will not allow data entering the network along that connection to exceed the bandwidth specified by the admission level. Specification of admission levels may help to reduce congestion in the network that would otherwise result from more data being admitted into the network than can be handled within the bandwidth capacity of the network elements.
Routes and admission levels for connections may be chosen through a number of mechanisms or algorithms, and may be allocated as the network receives requests to set up connections. Connections may be set up to handle a certain amount of bandwidth determined either through a statistical estimation of the demand for that connection, or through an explicit request for a given bandwidth through a Service Level Agreement (SLA).
The routings for connections (e.g., physical or virtual) in a connection-oriented network typically remain unchanged for a time after they are set up. However, at some time after they are set up, there may be a need to change the routings and/or admission levels for some or all connections in the network. This may be, for example, because some more optimal routing and admission configuration has been discovered, and because Service Level Agreements (SLAs) have changed, because estimated bandwidth demands have changed, or because some components of the network need to be replaced. To perform the change of routings and/or admission levels, a planned outage may be required, and routings changed to avoid the network elements to be taken down.
To provide high quality-of-service (QoS) on a data network (e.g., for voice transmissions or financial data transmissions), it is desirable that data connections in a network do not break or become congested, even for short periods of time. Currently, even if it is the case that all connections under a current routing and admission configuration and under a desired routing and admission configuration are able to provide the desired bandwidths, guarantees of avoidance of connection congestion or breakdown are difficult during a changeover from the current to the desired configuration. This is because routing and admission changes are typically performed in a distributed fashion by the source nodes of the connections using the relevant routings and admissions. Because these source nodes are distributed throughout the network, it is not a simple matter to synchronize the changes so that they all take place simultaneously. Therefore, there is a possibility that the network will exist, at least for a time, in intermediate configurations in which the routings and admissions are not correctly coordinated, leaving some connections broken or with insufficient bandwidth.